1. Technical Field
The present invention relates to an atomic resonance transition device, an atomic oscillator, an electronic apparatus, and a moving object.
2. Related Art
An atomic oscillator that oscillates based on energy transition in an alkali metal atom, such as rubidium and cesium is known to have a precise oscillation characteristic for a long period.
In general, the principle on which an atomic oscillator operates is classified roughly into a method using a double resonance phenomenon induced by light or a microwave and a method using coherent population trapping (CPT) induced by two light fluxes having wavelengths that are different from each other.
In an atomic oscillator based on each of the methods, it is typical that an alkali metal is sealed in a gas cell (an atom cell) and the gas cell is heated by a heater to a predetermined temperature to maintain the alkali metal in a constant gaseous state.
In an atomic oscillator of this type, a coil is disposed around the gas cell and caused to produce a steady magnetic field that causes a plurality of degenerated energy levels of the alkali metal atoms in the gas cell to split (Zeeman splitting), as disclosed in JP-A-2010-287937. For example, in the atomic oscillator described in JP-A-2010-287937, the magnetic field in the gas cell is homogenized for improved frequency stability.
As the size of an atomic oscillator has been required to be reduced in recent years, it has also been desired to reduce the size of the gas cell and the distance between the gas cell and a light source. A shorter distance between the gas cell and the light source, however, prevents a collimator lens from being disposed between the gas cell and the light source or the light in the gas cell from being collimated when a collimator lens is provided. As a result, a phenomenon called a light shift in which an increase in light level density increases the frequency even when the magnetic field in the gas cell is homogenized. This distorts the shape of an EIT signal produced by an atomic resonance phenomenon which results in a degradation in the frequency stability.